Logoff reminder

My manager has ask me to have the system babysit his frontdesk employees. He wants me to send a system message at logoff to remind them to punch the time clock. Is there another way to do this other than thru logoff scripts. There is a logoff script in effect but just to clean up network drive and printer connections. He latter ask if I could send them a message at a specific time to remind them to preform other duties. Any suggestions
rbrowning@pirentals.com